1. Field of the Invention
The present invention relates to a digital image recording system which reads an original image with an optical sensor to provide image data. This digital image recording system also compresses the image data as read, stores it into a recording medium, such as a semiconductor memory, a magnetic disk, etc., and if required, is capable of copying and outputting the image data.
2. Discussion of the Related Art
Recent image recording devices, such as a copying machine, employ digital image processing technology and are capable of many types of edit functions. For example, the image recording devices may perform enlargement/reduction, turning of an image, trimming an image to pick up and output only a desired area in an image, masking to remove only a desired area in an image, color change to change one color to another, and "cut and paste" to pick up an image within a desired area on a document and put that image into a desired area on another document.
In the above mentioned image recording apparatus, it is very frequently required to copy a plurality of documents and to produce a plurality of copies of each document in a preset order of pages. This function of the image recording system will be referred to as a recirculating document handling (RDH) function. In order to realize the RDH function in a conventional image recording apparatus, it is required to repeat, the number of times equal to that of copies, the operation of feeding an original document in an order of pages to obtain one copy. In this case, it takes a very long time, and each sheet of the document must be fed by an automatic document feeder (ADF) the number of times equal to that of copies. This greatly increases the risk that the document will be torn or wrinkled.
Further, with a sorter, each page of an original document is read a predetermined number of times, e.g., N times. Each time an image is read, it is copied onto copy sheets or papers that are discharged into N bins of the sorter in the image record section to obtain a plurality of copies in a predetermined order of pages on the basis of the original document consisting of a plurality of pages. In this case, damages to the document can be limited within the minimum since the document is fed only once. However, bins whose number is equal to that of copies are required, the system will be large-sized in order to obtain a large number of copies. Further, in case where the subsequent processing such as stapling and binding is performed, the processing must be performed in each bin or outside of each bin. Such a processing arises a trouble and prevents an automatization of the system.
Furthermore, where an instruction according to a copy job is incorrect, it is delayed to recognize that because of much time for completing one copy, and a large subsequent adjustment may be required.
A conventional digital image recording system that electronically implements the RDH function is shown in FIG. 6.
Ige data outputted from an image read section 51 is applied to a compressor 52 where it is compressed by a specified amount. The compressed data is then written into a page buffer 54 of a storage unit 53. The storage unit 53 preferably has a large memory capacity in order to store image data for a large number of documents. Usually, a magnetic memory, such as a hard disk (HD) 55, is used as shown. The access time of the HD 55 is about 1 Mbyte/sec. This access time differs from the transfer speed of the input image data. The page buffer 54 is provided to cop with the speed difference.
The compressed data temporarily stored in the page buffer 54 is sequentially stored into the HD 55. After the image data of the set of documents is completed, the image data stored in the HD 55 is read out page by page, and stored into the page buffer 54. After a preset amount of image data is stored, an expander 56 sequentially fetches the compressed image data from the page buffer 54, decodes (expands) the fetched image data, and outputs the decoded image data to an image record section 57. In the final stage, the image record section 57 produces a hard copy.
With such an arrangement, images on a number of documents are read one time, and the image data, as read, is stored into the HD 55. Then, the image data is read out of the HD 55 page by page. In this way, a number of documents are copied, and a desired number of copies of each document is output in a desired order. Thus, the RDH function can be electronically realized, providing easy copying.
There are many types of documents to be copied, such as character documents to be expressed in only two gray levels, black and white; photographic documents to be expressed in multiple gray levels (referred to as a multi-gradation); and documents in which only a specific area or areas must be colored for emphasis purposes. The character document must be outputted at a high speed. The photograph document must be outputted with a high picture quality even if there is a slight sacrifice in the copy rate.
In the conventional image data recording system shown in FIG. 6, the amount of image data outputted from the image read section 51 is fixed. For example, the data amount per pixel is fixed at M bits, and therefore process speed is fixed. Accordingly, the above documents may not be copied properly by the above described image recording apparatus.
To cope with these problems, the following solutions have been proposed. To speed up the data transfer, the number of bits for one pixel is set to be as small as possible, for example, 2 bits for one pixel. However, if the number of bits per pixel is 2, photographs cannot be copied with high quality. To improve the picture quality, the number of bits for one pixel must be increased, for example, to 8 bits for one pixel. This can improve the picture quality, but reduces the effective data transfer speed, and bits are used unnecessarily for processing an image of a document that could have been expressed with a smaller number of bits.